Maybe an experienced admiral from the Earth Defense Fleet. She would bring her strategic knowledge to the table when dealing with the complex political and military situations in the Star Wars universe. And she could also form alliances with characters like Leia Organa.
Perhaps the Earth Defense Fleet could get stranded in the Star Wars universe. They then have to use their unique Earth - based technology in combination with Star Wars tech to find their way back home while also getting involved in local conflicts.
A young Earthling who is discovered to be extremely Force - sensitive could be a main character. He or she could be mentored by an old Jedi master and go on a journey to learn about the Force and their place in the Star Wars universe.
One main character could be a military general on Earth. He has extensive combat experience and is tasked with leading the defense against the Star Wars invaders. Another could be a young orphan who discovers he has an uncanny ability to interact with the Force, which makes him a key figure in the fight. And perhaps a Jedi who has been exiled to Earth long ago and now has to step up to help his new home planet.
A character could be a Force - sensitive child from the United Earth Empire. He was born with this power but was hidden away on Earth. When the Empire discovers his abilities, they want to use him as a weapon. However, he is befriended by a group of rebels who help him understand the true nature of the Force and fight against the Empire's evil plans.
One possible main character could be an Earth scientist. They would be in a unique position to study the Empire's technology and try to find a way to defend Earth.
A likely main character could be a scientist from Earth who is excited about the opportunity to study the advanced technology of the Star Wars universe. They would be in the middle of the relationship between Earth and the CIS, trying to use the alliance for scientific progress. Also, a CIS spy on Earth could be a main character, tasked with ensuring Earth's loyalty and reporting any signs of betrayal.
Luke Skywalker could be one of the main characters. He might come to Earth to spread the teachings of the Jedi. Another could be Darth Vader, if he somehow survived and ended up on Earth, causing chaos and trying to rule over the planet.
One possibility for the main character in a 'Star Wars Earth First Contact' fanfic could be a Mandalorian. Mandalorians are known for their combat skills and their unique code of honor. Landing on Earth, they would face a whole new set of challenges and cultures. They might initially see Earth as a potential place for conquest or plunder but then develop a more complex relationship with the planet. Additionally, an astromech droid like R2 - D2 could be a main character. It could communicate in its own way with Earth technology and help bridge the gap between the two worlds, all while having its own little droid adventures on Earth.
It could be an ordinary human on Earth who rises to become a hero against the Empire. Maybe a scientist who figures out a way to counter the Empire's force powers.
Luke Skywalker is often popular. He can be reimagined in an earth - setting, perhaps as a young man who discovers his latent 'Jedi' abilities while living an ordinary life. His journey from being a regular person to embracing his powers can be really engaging.